ColdFusion code for Plupload file uploading including chunked transfers

upload.cfc

<cfcomponent>

  <cffunction name="upload" access="remote" returntype="struct" returnformat="json" output="false">
    <cfscript>
      var uploadDir = expandPath('.') & '/uploads/'; // should be a temp directory that you clear periodically to flush orphaned files 
      var uploadFile =  uploadDir & arguments.NAME;
      var response = {'result' = arguments.NAME, 'id' = 0};
      var result = {};
      // if chunked append chunk number to filename for reassembly
      if (structKeyExists(arguments, 'CHUNKS')){
        uploadFile = uploadFile & '.' & arguments.CHUNK;
        response.id = arguments.CHUNK;
      }
    </cfscript>		
		
    <!--- save file data from multi-part form.FILE --->
    <cffile action="upload" result="result" filefield="FILE" destination="#uploadFile#" nameconflict="overwrite"/>
		
    <cfscript>
      // Example: you can return uploaded file data to client 
      response['size'] = result.fileSize;
      response['type'] = result.contentType;
      response['saved'] = result.fileWasSaved;
			
      // reassemble chunked file
      if (structKeyExists(arguments, 'CHUNKS') && arguments.CHUNK + 1 == arguments.CHUNKS){
        try {
          var uploadFile = uploadDir & arguments.NAME; // file name for reassembled file - if using a temp directory then this should be the final output path/file
          if (fileExists(uploadFile)){
            fileDelete(uploadFile); // delete otherwise append will add chunks to an existing file
          }

          var tempFile = fileOpen(uploadFile,'append');
          for (var i = 0; i < arguments.CHUNKS; i++) {
            var chunk = fileReadBinary('#uploadDir#/#arguments.NAME#.#i#');
            fileDelete('#uploadDir#/#arguments.NAME#.#i#');
            fileWrite(tempFile, chunk);
          }
          fileClose(tempFile);
	}
        catch(any err){
          // clean up chunks for incomplete upload
          var d = directoryList(uploadDir,false,'name');
          if (arrayLen(d) != 0){
            for (var i = 1; i <= arrayLen(d); i++){
              if (listFirst(d[i]) == arguments.NAME && val(listLast(d[i])) != 0){
                fileDelete('#uploadDir##d[i]#');
              }
            }
          }

          // you could add more error handling and return info from err 
          response = {'error' = {'code' = 500, 'message' = 'Internal Server Error'}, 'id' = 0};  
        }
      }
      return response;
    </cfscript>
  </cffunction>

</cfcomponent>

I'm having issues getting the json messages in the cfreturn statement to display on the page with the pluploader.

                $(document).ready(function() {
                    $("##pluploader").pluploadQueue({       
                            runtimes : 'html5',
                            url : 'photosMultiUpload.cfc?method=upload',
                            max_file_size : '7mb',
                            chunk_size : '1mb',
                            unique_names : true,
                            dragdrop : true,
                            filters : [
                                    {title : "Image files", extensions : "jpg,gif,png,jpeg"}
                            ],
                            FilesAdded: function(editor,files){
                                alert(files);
                            }
                        ,Error: function(up, err) {
                            alert(err);
                        } 
                    ,FileUploaded: function(up, file, info) {
                        alert(file);
                    }
                });       
                });

I have the cftry/cfcatch as in your example. The uploader page displays a green tick and 100% uploaded and the firebug shows my json message:
error
Object { message="Internal Server Error", code=500}

message
"Internal Server Error"

code
500

Any advice?

This script checks for any already-uploaded file with an identical filename to that of the file that the user is uploading now. There might be an issue with filename conflicts. User (A) could have uploaded "selfie.jpg" and then User (B) uploads a totally different "selfie.jpg." The script deletes the file on the assumption that it's the same file, which in this case would be inaccurate. Why not create a new subdirectory named after a UUID, save the newly uploaded file into the new directory, then send the path to the uploaded file back to the user? Seems safer than just deleting an already-uploaded file.